Apparatus and method for filtering voiceband and metering tone frequencies of a mixed voice/data signal

Abstract

An apparatus and method provide for filtering of voiceband and specified tone frequencies of a mixed voice/data signal, such as an Asymmetric Digital Subscriber Line (ADSL) signal. A lowpass filter section passes voiceband content of the mixed signal and suppresses mixed signal content having frequencies falling within a databand of the mixed signal. A bandpass filter section is coupled to or integral with the lowpass filter section and passes the specified tone frequency, such as a metering or billing tone frequency. The lowpass and bandpass filter sections exhibit a combined frequency response that provides for a stopband between the voiceband and the metering tone frequency. The bandpass filter section effectively detunes a frequency response of the lowpass filter section to provide for the stopband. The stopband preferably provides for an insertion loss of 3 dB or greater between the voiceband and the metering tone frequency, and suppresses undesirable mixed signal content having frequencies falling within the stopband. The lowpass filter section and the bandpass filter section may each be implemented to include only passive components, such as passive magnetic components.

What is claimed is:  
     
       1. A circuit for filtering both voiceband and metering tone frequencies of a mixed voice/data signal the circuit comprising: 
       a lowpass filter section that passes voiceband content of the mixed signal, the lowpass filter section suppressing mixed signal content having frequencies falling within a databand of the mixed signal;  
       a bandpass filter section coupled with the lowpass filter section, the bandpass filter section passing the metering tone frequency, the lowpass and bandpass filter sections farther exhibiting a frequency response that provides for a stopband between the voiceband and the metering tone frequency, the stopband suppressing undesirable mixed signal content associated with frequencies falling within the stopband; and  
       wherein the bandpass filter section is integral with the lowpass filter section.  
     
     
       2. The circuit of  claim 1 , wherein the lowpass filter section and the bandpass filter sections each comprise only magnetic components. 
     
     
       3. The circuit of  claim 1 , wherein the bandpass filter section comprises passive magnetic components. 
     
     
       4. The circuit of  claim 1 , wherein the bandpass filter section effectively detunes a frequency response of the lowpass filter section to provide for the stopband between the upper and of the voiceband and the metering tone frequency. 
     
     
       5. The circuit of  claim 1 , wherein the bandpass filter section comprises a bandpass resonator. 
     
     
       6. The circuit of  claim 1 , wherein the bandpass filter section comprises a resonant tuned bandpass filter centered around the metering tone frequency. 
     
     
       7. The circuit of  claim 1 , wherein the lowpass filter section passes voiceband content of the mixed signal to about 4 kHz. 
     
     
       8. The circuit of  claim 1 , wherein the lowpass and bandpass filter sections comprise a plurality of stages, each stage comprising a pair of coupled inductive elements and a load capacitor. 
     
     
       9. The circuit of  claim 8 , wherein the pair of coupled inductive elements and the load capacitor of at least one of the stages have respective inductance and capacitance values differing from those of other stages. 
     
     
       10. The circuit of  claim 1 , wherein the bandpass filter section passes a metering tone having a frequency specified by a telecommunications standard. 
     
     
       11. The circuit of  claim 1 , wherein the bandpass filter section passes a metering tone having a frequency of about 12 kHz or about 16 kHz. 
     
     
       12. The circuit of  claim 1 , wherein the bandpass filter section passes a metering tone having a frequency of about 20 kHz. 
     
     
       13. The circuit of  claim 1 , wherein the databand comprises mixed signal content having frequencies of about 30 kHz or higher. 
     
     
       14. The circuit of  claim 1 , wherein the circuit is configured as a 3-port filter, the lowpass and bandpass filter sections defining two ports of the 3-port filter and a highpass filter section defining a third port of the 3-port filter. 
     
     
       15. The circuit of  claim 1 , wherein the mixed voice/data signal conforms to an Asymmetrical Digital Subscriber Line (ADSL) standard. 
     
     
       16. A circuit for filtering both voiceband and metering tone frequencies of a mixed voice/data signal the circuit comprising: 
       a lowpass filter section that passes voiceband content of the mixed signal, the lowpass filter section suppressing mixed signal content having frequencies falling within a databand of the mixed signal; and  
       a bandpass filter section coupled with the lowpass filter section, the bandpass filter section passing the metering tone frequency, the lowpass and bandpass filter sections further exhibiting a frequency response that provides for a stopband between the voiceband and the metering tone frequency, the stopband suppressing undesirable mixed signal content associated with frequencies falling within the stopband; and wherein the stopband associated with the lowpass and bandpass filter sections provides for an insertion loss of 3 dB or greater between the voiceband and the metering tone frequency.  
     
     
       17. A method of filtering voiceband and metering tone frequencies of a mixed voice/data signal, comprising: 
       passively filtering, using a lowpass filtering response, the mixed voice/data signal to pass voiceband content of the mixed voice/data signal and to suppress mixed signal content having frequencies falling within a databand of the mixed signal;  
       passively filtering, using a bandpass filtering response, the mixed voice/data signal to pass the metering tone frequency;  
       detuning the low-pass filtering response to produce a stopband between an upper end of the voiceband and the metering tone frequency; and  
       suppressing, using the detuned low-pass filtering response, undesirable mixed signal content associated with frequencies falling within the stopband.  
     
     
       18. The method of  claim 17 , wherein the stopband provides for an insertion loss of 3 dB or greater between the voiceband and the metering tone frequency. 
     
     
       19. The method of  claim 17 , wherein voiceband content of the mixed signal comprises frequencies to about 4 or 5 kHz. 
     
     
       20. The method of  claim 17 , wherein passively filtering the mixed voice/data signal to pass voiceband content of the mixed voice/data signal comprises inductively and capacitively filtering the mixed voice/data signal to pass voiceband content of the mixed voice/data signal. 
     
     
       21. The method of  claim 17 , wherein the metering tone defines a frequency specified by a telecommunications standard. 
     
     
       22. The method of  claim 17 , wherein the metering tone defines a frequency of about 12 KHz or about 16 kHz. 
     
     
       23. The method of  17 , wherein the metering tone defines a frequency of about 20 kHz. 
     
     
       24. The method of  claim 17 , wherein passively filtering the mixed voice/data signal to pass the metering tone frequency comprises inductively and capacitively filtering the mixed voice/data signal to pass the metering tone frequency. 
     
     
       25. The method of  claim 17 , wherein the mixed voice/data signal conforms to an Asymmetrical Digital Subscriber Line (ADSL) standard. 
     
     
       26. The method of  claim 17 , wherein the databand comprises mixed signal content having frequencies of about 30 kHz or higher. 
     
     
       27. The method of  claim 17 , further comprising filtering, using a highpass filtering response, the mixed voice/data signal to pass databand content of the mixed voice/data signal and to suppress mixed signal content having frequencies falling below the databand. 
     
     
       28. A circuit for filtering both voiceband and metering tone frequencies of a mixed voice/data signal, the circuit comprising: 
       an input interface that receives the mixed voice/data signal;  
       a low frequency filter circuit including an input coupled to the input interface, the low frequency filter circuit comprising:  
       a lowpass filter section that passes voiceband content of the mixed signal, the lowpass filter section suppressing mixed signal content having frequencies falling within a databand of the mixed signal; and  
       a bandpass filter section coupled with the lowpass filter section, the bandpass filter section passing the metering tone frequency, the lowpass and bandpass filter sections further exhibiting a frequency response that provides for a stopband between the voiceband and the metering tone frequency, the stopband suppressing undesirable mixed signal content associated with frequencies falling within the stopband;  
       a high frequency filter circuit including an input coupled to the input interface, the high frequency filter circuit suppressing mixed signal content having frequencies falling below the databand;  
       an output interface having a low frequency output coupled to an output of the lowpass filter section and a high frequency output coupled to an output of the bandpass filter section, a voiceband signal provided at the low frequency output of the output interface and a data signal provided at the high frequency output of the output frequency; and  
       wherein the bandpass filter section is integral with the lowpass filter section.  
     
     
       29. The circuit of  claim 28 , wherein the lowpass filter section and the bandpass filter section each comprise only passive components. 
     
     
       30. The circuit of  claim 28 , wherein the bandpass filter section comprises passive magnetic components. 
     
     
       31. The circuit of  claim 28 , wherein the bandpass filter section comprises a bandpass resonator. 
     
     
       32. The circuit of  claim 28 , wherein the bandpass filter section passes a metering tone having a frequency specified by a telecommunications standard. 
     
     
       33. The circuit of  claim 28 , wherein the bandpass filter section passes a metering tone having a frequency of about 12 kHz or about 16 kHz. 
     
     
       34. The circuit of  claim 28 , wherein the bandpass filter section passes a metering tone having a frequency of about 20 kHz. 
     
     
       35. The circuit of  claim 28 , wherein the lowpass and bandpass filter sections comprise a plurality of stages, each stage comprising a pair of coupled inductive elements and a load capacitor. 
     
     
       36. The circuit of  claim 35 , wherein the pair of coupled inductive elements and the load capacitor of at least one of the stages have respective inductance and capacitance values differing from those of other stages. 
     
     
       37. The circuit of  claim 28 , wherein the databand comprises mixed signal content having frequencies of about 30 kHz or higher. 
     
     
       38. The circuit of  claim 28 , wherein the mixed voice/data signal conforms to an Asymmetrical Digital Subscriber Line (ADSL) standard. 
     
     
       39. The circuit of  claim 28 , wherein the input interface receives the mixed voice/data signal from a POTS (Plain Old Telephone Service) connection. 
     
     
       40. The circuit of  claim 28 , wherein the input interface receives the mixed voice/data signal from a connection having a fixed or complex impedance. 
     
     
       41. A circuit for filtering both voiceband and metering tone frequencies of a mixed voice/data signal, the circuit comprising: 
       an input interface that receives the mixed voice/data signal;  
       a low frequency filter circuit including an input coupled to the input interface, the low frequency filter circuit comprising:  
       a lowpass filter section that passes voiceband content of the mixed signal, the lowpass filter section suppressing mixed signal content having frequencies falling within a databand of the mixed signal; and  
       a bandpass filter section coupled with the lowpass filter section, the bandpass filter section passing the metering tone frequency, the lowpass and bandpass filter sections further exhibiting a frequency response that provides for a stopband between the voiceband and the metering tone frequency, the stopband suppressing undesirable mixed signal content associated with frequencies falling within the stopband;  
       a high frequency filter circuit including an input coupled to the input interface, the high frequency filter circuit suppressing mixed signal content having frequencies falling below the databand;  
       an output interface having a low frequency output coupled to an output of the lowpass filter section and a high frequency output coupled to an output of the bandpass filter section, a voiceband signal provided at the low frequency output of the output interface and a data signal provided at the high frequency output of the output frequency; and  
       wherein the stopband associated with the lowpass and bandpass filter sections provides for an insertion loss of 3 dB or greater between the voiceband and the metering tone frequency.